The present invention relates to a connecting member for connecting electronic devices, and more particularly to a connecting member for connecting pads facing each other.
A conventional technique for connecting a flexible substrate and a mounting substrate is disclosed in U.S. Pat. No. 5,261,155.
Referring to FIG. 6 of the reference, a solder member 32 and a solder paste 27 connect conductor 39 of a flexible substrate 31 and a conductive pad 23 of a substrate 13. The solder member 32 and the solder paste 27 form a solder bump.
Referring to FIGS. 4 and 5 of U.S. Pat. No. 5,261,155, the flexible substrate 31 and the substrate 13 are connected by the following steps.
In a first step, the solder paste 27 is provided on the conductive pad 23 of the substrate 13.
In a second step, the solder member 32 is positioned on the solder paste 27. Thereafter, the flexible substrate 31 is positioned so that the conductor 39 faces the solder member 32.
In a third step, the solder member 32 and the solder paste 27 are heated to melt and connect the conductor 39 and the conductive pad 23.
Referring to FIG. 9, the reference further discloses a through-hole provided in the flexible substrate 31. The through-hole is not tapered.
The aforementioned conventional structure has the following problems.
First, the heights of the bumps (i.e., the gap between the conductor 39 and the conductive pad 23) vary with the positions thereof when the flexible substrate 31 warps, and thus become uneven and have a nonuniform height.
Second, when the flexible substrate 31 is pressed against the substrate 13 during heating to enhance the flatness thereof, the solder member 32 and the solder paste 27 are squeezed. The squeezed solder member 32 and solder paste 27 spreads over the substrates 31 and 13, thereby short-circuiting conductor patterns provided on the substrates.
The above-mentioned first and second problems are especially serious when the conventional technique is applied to a fine pitch soldering.
Third, the mechanical strength of the solder bump is weak.
Fourth, a faulty connection of the solder bump is not easily detected because the solder bump is obscured under the flexible substrate 31.
Fifth, when the flexible substrate 31 is pressed against the substrate 13, the squeezed solder spreads over the upper surface of the flexible substrate 31 via the through-hole.